Allow the vizzini module to be installed side-by-side with cdc-acm.

 * Use a dynamically allocated major device number.

 * Use the tty name of /dev/ttyVIZx so it doesn't conflict with other devices.

 * Create a udev rule which makes sure the device is bound to the vizzini
   module. This is needed if the vizzini module is loaded *after* the cdc-acm
   module as drivers are checked in the order they have been loaded and the
   cdc-acm registers for the device class exported by the device.

 * Adding slightly better debug messages.